Compartmented thermoplastic pellets

Abstract

Apparatus and method for the production of hopper feedable thermoplastic pellets having zones or compartments which contain physically separated reactants which react only after being melt-mixed, as in a screw type extruder, reciproscrew injection machine, or similar device which heat forms pellets into a larger mass. This new class of thermoplastic molding materials relies mainly on the relatively slow reaction kinetics of contained large molecule molding materials to provide a time interval after melt-mixing of zoned pelletized reactants in an extruder barrel or injection molding machine. During this time period, the thermoplastic molding material is easily filled into injection molds. As the reaction progresses, the material becomes more viscous and such flow is difficult or impossible. The involved reactions may continue after demolding at room temperature during a post molding cure, or appliance service generated heat may cause post molding cure. Where a delayed reaction involves crosslinking and/or additional polymer molecular growth after molding, such crosslinking can bond adjacent molecules and reduce or prevent stress memory warpage of molded parts. Fibrous reinforcements may be included to aid in reducing post molding warpage. Foaming agents contained can, when molded by the Bradt Process, virtually eliminate weld lines in molded parts.

What is claimed is: 
     
       1. A process for manufacturing reproducibily zoned and structured thermoplastic molding pellets comprising the steps of combining at least two dissimilar chemically interreactive, easy flowing thermoplastic moldable materials into an aggregated continuous form, and reducing the continuous form into identically shaped and structured individual pellets with the dissimilar materials isolated from one another within separate zones in the individual pellets. 
     
     
       2. The process of claim 1 wherein the step of combining comprises providing a central strand and forming concentric layers of dissimilar materials about the central strand. 
     
     
       3. The process of claim 1 wherein certain zones contain chemically inert fibrous reinforcing material. 
     
     
       4. The process of claim 1 wherein certain zones contain foaming agents. 
     
     
       5. The process of claim 1 wherein at least two of the materials are chemically interreactive when mixed and heated. 
     
     
       6. The process of claim 1 wherein the step of combining comprises stacking together a plurality of relatively flat sheets of dissimilar moldable materials, and the step of reducing includes dicing the stack into individual generally cubic pellets. 
     
     
       7. The process of claim 1 wherein the step of combining comprises providing an elongated tube having a plurality of elongated isolated compartments therein and separating at least two interactive materials by placing each in a separate compartment, and the step of reducing includes severing the tube into relatively short segments and pinch sealing the resulting tube segment ends. 
     
     
       8. The process of molding relatively high large molecular weight containing plastic products comprising the steps of: melting a plurality of dissimilar chemically interreactive relatively low molecular weight plastic materials located in distinct zones within the molding pellets;   mixing the melted dissimilar materials;   quickly molding the mixed melted dissimilar materials into a plastic product;   allowing a molecular growth chemical reaction within the molded product to continue after molding to create a long-chain molecule within the molded product.   
     
     
       9. The process of claim 8 wherein the step of molding is performed before significant molecular growth of the mixed materials occurs. 
     
     
       10. The process of claim 8 wherein the step of quickly molding is performed by extrusion.